U.S. patent application number 10/699176 was filed with the patent office on 2004-06-17 for tunable wavelength semiconductor laser diode.
Invention is credited to Kim, Hyun-Soo, Kim, Jong-Hoi, Kim, Kang-Ho, Kwon, Oh-Kee, Oh, Kwang-Ryong.
Application Number | 20040114644 10/699176 |
Document ID | / |
Family ID | 32501389 |
Filed Date | 2004-06-17 |
United States Patent
Application |
20040114644 |
Kind Code |
A1 |
Kwon, Oh-Kee ; et
al. |
June 17, 2004 |
Tunable wavelength semiconductor laser diode
Abstract
Disclosed is a tunable wavelength semiconductor laser diode
which comprises a FP(fabry-parrot) laser diode array for producing
at least two light beams, a combiner for combining the light beams
output by an end of the laser diode array, a lens for collimating
the light beams output by another end thereof, a grating for
diffracting the light beams collimated by the lens, and a reflector
for reflecting the light beams diffracted by the grating to feed
the reflected light beams back to the laser diode array.
Inventors: |
Kwon, Oh-Kee; (Anyang-city,
KR) ; Kim, Kang-Ho; (Daejeon-city, KR) ; Kim,
Hyun-Soo; (Daejeon-city, KR) ; Kim, Jong-Hoi;
(Daejeon-city, KR) ; Oh, Kwang-Ryong;
(Daejeon-city, KR) |
Correspondence
Address: |
BLAKELY SOKOLOFF TAYLOR & ZAFMAN
12400 WILSHIRE BOULEVARD, SEVENTH FLOOR
LOS ANGELES
CA
90025
US
|
Family ID: |
32501389 |
Appl. No.: |
10/699176 |
Filed: |
October 30, 2003 |
Current U.S.
Class: |
372/20 ;
372/97 |
Current CPC
Class: |
H01S 5/4062 20130101;
H01S 5/143 20130101; H01S 5/026 20130101; H01S 5/141 20130101 |
Class at
Publication: |
372/020 ;
372/097 |
International
Class: |
H01S 003/10; H01S
003/082 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 12, 2002 |
KR |
2002-79228 |
Claims
What is claimed is:
1. A tunable wavelength semiconductor laser diode comprising: a
laser diode array for producing at least two light; a combiner for
combining the light beams output by an end of the laser diode
array; a lens for collimating the light beams output by another end
thereof; a grating for diffracting the light beams collimated by
the lens; and a reflector for reflecting the light beams diffracted
by the grating to feed the reflected light beams back to the laser
diode array.
2. The laser diode of claim 1, wherein the laser diode includes a
multi-channel FP (fabry-parrot) laser diode array.
3. The laser diode of claim 1, wherein the combiner has an optical
waveguide configuration or an MMI (multimode interface) type
passive optical waveguide configuration.
4. The laser diode of claim 1, wherein a wavelength of the light
beam output to the fiber is controlled by an arrangement interval
of the laser diode array.
5. The laser diode of claim 1, wherein a wavelength of the light
beam output to the fiber is controlled by a focal length of the
lens.
6. A tunable wavelength semiconductor laser diode comprising: a
multi-channel diode array for producing at least two light; an AWG
(array wavelength grating) for selecting one of the light beams
output by an end of the multi-channel diode array, and outputting
it to a fiber; a lens for collimating the light beam output by
another end thereof; a grating for diffracting the beam collimated
by the lens; and a reflector for reflecting the beam diffracted by
the grating, and feeding the light beam to a FP (fabry-parrot)
laser diode array.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to and the benefit of Korea
Patent Application No. 2002-79228 filed on Dec. 12, 2002 in the
Korean Intellectual Property Office, the content of which is
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] (a) Field of the Invention
[0003] The present invention relates to a tunable wavelength
semiconductor laser diode used for a light source in a WDM
(wavelength division multiplexing) system. More specifically, the
present invention relates to a tunable wavelength semiconductor
laser diode for using in an external resonator type including a
laser diode, a lens, a grating, and an external reflector,
reflecting a beam output from the laser diode to the external
reflector, and feeding the beam back to the semiconductor
resonator, thereby tuning a wavelength of the output beam at a
specific region.
[0004] (b) Description of the Related Art
[0005] In a WDM system, it is required for a tunable wavelength
semiconductor light source to have a narrow spectral line width and
wide wavelength tunability in an operation region so as to realize
continuous wavelengths without mode hopping over a tuning
range.
[0006] An external resonator type tunable wavelength laser diode
advantageously has broader and more continuous wavelength
tunability (>100 nm), narrow spectral line width (<2 MHz) by
1/10 to 1/100 times, and a high SMSR (side mode suppression ratio,
>40 dB) than a distributed bragg reflector using a sampled
grating, and in particular, a Littman type external resonator
provides an unvaried direction of an output beam at the time of
varying a wavelength thereby also obtaining good directivity.
[0007] As to a conventional configuration of the Littman type
external resonator shown in FIG. 4, the light output from a FP
(Fabry-Parrot) laser diode 2 is collimated by a lens 4 and provided
to a grating 6, and angle and intensity of the diffracted beam
induced by the grating are determined according to a wavelength and
an angle of an incident beam, and a period of the grating 6. A
corresponding diffraction principle follows the equation
m.lambda.=b(sin .alpha.+sin .beta.) where m is a diffraction order,
b is a period of a grating, .alpha. is an angle of incident beam,
and .beta. is an angle of the diffraction beam.
[0008] A 0-order diffraction beam by the grating is focused through
an output end lens 8, and is coupled to a fiber 10, and the
+1-order diffraction beam is reflected from an external reflector
12 and fed back to the laser diode 2. That is, when the reflector
12 is rotated, wavelengths vertically provided to a mirror surface
of the reflector with respect to the +1-order diffraction beam of
the grating 6 are selectively fed back to the laser diode 2.
[0009] In this instance, rotation .DELTA..theta. of the reflector
12 is defined as the .DELTA..theta.=.DELTA..beta. since the
rotation of the reflector is matched to the variation of the
+1-order diffraction angle, and the variation of the +1-order
diffraction angle in the equation is produced as
.DELTA..beta.=m.DELTA..lambda./b cos .beta..
[0010] In further detail to the variation of the diffraction angle
with reference to FIG. 5, when the beam B1 output from the laser
diode 2 is provided with an angle .alpha. with respect to a
perpendicular axis 6c of the grating surface, the +1-order
diffraction beam is refracted by an angle of .beta. with respect to
the perpendicular axis 6c and vertically provided to the reflector
12, and the 0-order diffraction beam is diffracted with an angle of
-.alpha. and output through the fiber 10.
[0011] The +1-order beam input to the reflector 12 is totally
reflected to be a feedback beam B2 that is output with an angle of
.beta. with respect to the grating 6, the feedback beam B2 input to
the grating 6 with the above-noted angle is refracted with an angle
of .alpha. based on the above-described equation with the angle of
.beta. to be fed back to the laser diode 2, and the 0-order
diffraction of the feedback beam B2 refracted with the angle of
-.beta. is lost.
[0012] In the above-mentioned process, when the reflector 12 is
rotated, the angle a of the +1-order diffraction beam of the beam
B1 vertically provided on the reflector is required to be changed,
and hence, the wavelengths of the incident beams on the same angle
of incidence are varied according to the diffraction principle.
[0013] In general in a WDM system with a wavelength of 1.55 .mu.m,
it is required to rotate a rotary variance .DELTA..theta. of the
reflector 12 by +2.1 degrees (a total of 4.2 degrees) in order to
produce a wavelength tuning of 60 nm when the angle of incidence of
the grating 6 is 80 degree and the period of the grating 6 is 1
.mu.m.
[0014] The above-described external resonator type tunable
wavelength laser diode with wavelength tuning characteristics that
depend on the rotation of the reflector cannot avoid problems such
as stability deterioration caused by mechanical vibration of the
reflector at the time of tuning the wavelength of the laser diode,
and accordingly, long-time reliability is lowered.
[0015] A multichannel laser diode array solves the above-noted
problems caused by the mechanical vibration of the reflector.
[0016] FIG. 6 shows a general configuration of a multichannel FP
laser diode array.
[0017] The basic configuration of FIG. 6 corresponds to that of
FIG. 4, and in addition, a FP laser diode array 14 is adopted for a
light source, a lens 4 is used to collimate beams output from the
laser diode array 14, the 0-order diffraction beam is output as
optical loss in a grating 6, and part of the +1-order diffraction
beams that has passed through the fixed half mirror reflector 16 is
output to the fiber 10 through a lens 18 and another part thereof
is reflected and fed back.
[0018] A principle of a tunable wavelength on an array interval has
been applied to the above-configured multi-channel laser diode.
That is, as shown in FIG. 7, an angle of a beam provided to the
grating surface a is varied according to an arrangement interval of
the laser diode array 14, and corresponding equations are given as
.DELTA..alpha.=.alpha.1-.alpha.2- =.phi., and accordingly, it is
given that D=.function. tan .PHI. where D is an array interval,
.function. is a focal length, and .PHI. is a variance of an
incident angle. For example, the wavelength interval of 0.8 nm
(.DELTA..function.=(C/.lambda..sup.2).DELTA..lambda. where C is the
speed of light, .function. is a frequency, and .lambda. is a
wavelength) is needed so as to maintain the channel spacing of 100
GHz in the WDM system in the wavelength of 1.55 .mu.m, and when the
variance of the incident angle is given as 0.264 degrees
(.DELTA..alpha.=.DELTA..lamb- da./d cos .alpha. where .alpha. is 80
degrees and d is given as 1 .mu.m) and the focal length between the
lens and the array is defined as 4.34 mm, the array distance D is
produced as 20 .mu.m.
[0019] The above-configured multi-channel FP laser diode array as a
tunable wavelength laser diode provides stable tuning
characteristics and high-speed operations since there is no need to
drive and rotate the reflector. However, since a number of
wavelength channels are proportionally corresponds to a number of
arrays, it is necessary to increase the number of channels and that
of arrays so as to widen the wavelength range, and a diameter of
the lens and an area of the grating accordingly increase, and the
total size of the device enlarges thereby restricting increase of
the wavelength tuning range.
[0020] Referring to FIG. 8 for increasing the wavelength tuning
range, a beam output from a DFB (distributed-feedback) laser diode
array 14 is passed through a lens 4, it is reflected according to a
rotary control by a reflector 12, and a wavelength output from a
specific channel is only output to a fiber 10 through an output end
lens 8.
[0021] This method advantageously provides a simple configuration
for controlling the current injected to DFB laser diodes with
different grating periods to tune wavelengths and change a
direction of a reflector, but it is difficult to manufacture the
desired DFB laser diode arrays, and it still remains as a problem
to provide a huge volume of DFB laser diodes of as many as the
number of wavelength channels.
[0022] As a result, the conventional single configuration of the
DFB laser diode requires a grating with a precise period of
substantially 1 .mu.m, and fine rotary characteristics of a
reflector, and the multichannel DFB laser diode array requires an
increase of a diameter of a lens as the number of arrays increases,
thereby limiting widening of a wavelength range, and it is needed
to provide a huge amount of DFB laser diode arrays of as many as
the number of channels.
SUMMARY OF THE INVENTION
[0023] It is an advantage of the present invention to provide a
tunable wavelength semiconductor laser diode for increasing a
period of a grating (>1 .mu.m) without requiring fine control of
a reflector to thus realize a wide tuning range.
[0024] In one aspect of the present invention, a tunable wavelength
semiconductor laser diode comprises: a laser diode array for
producing at least two light beams; a combiner for combining the
light beams output by an end of the laser diode array; a lens for
collimating the light beams output by another end thereof; a
grating for diffracting the light beams collimated by the lens; and
a reflector for reflecting the light beams diffracted by the
grating to feed the light beams back to the laser diode array.
[0025] The laser diode includes a multi-channel FP laser diode
array.
[0026] The combiner has optical passive waveguide couplers such as
a directional coupler and a MMI (Multi-Mode Interference)
coupler.
[0027] A wavelength of the light beam output to the fiber is
controlled by an arrangement interval of the laser diode array and
a focal length of the lens.
[0028] In another aspect of the present invention, a tunable
wavelength semiconductor laser diode comprises: a multi-channel FP
laser diode array; an AWG (arrayed waveguide grating) structure for
selecting one of the light beams output by an end of the
multi-channel FP laser diode array, and outputting it to a fiber; a
lens for collimating the light beam output by another end thereof;
a grating for diffracting the beam collimated by the lens; and a
reflector for reflecting the beam diffracted by the grating, and
feeding the light beam to a FP-laser diode array.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate an embodiment of
the invention, and, together with the description, serve to explain
the principles of the invention:
[0030] FIG. 1 shows a schematic diagram of a multi-channel FP laser
diode array of an external resonator type according to a first
preferred embodiment of the present invention;
[0031] FIG. 2 shows a schematic diagram of a multi-channel FP laser
diode array of an external resonator type according to a second
preferred embodiment of the present invention;
[0032] FIG. 3 shows spectral characteristics of the device
according to preferred embodiments of the present invention;
[0033] FIG. 4 shows a schematic diagram of a conventional Littman
type tunable wavelength semiconductor laser diode;
[0034] FIG. 5 shows a schematic diagram of a 0-order diffracted
beam and a +1-order diffracted beam between a grating and a
reflector as to a beam provided to the grating of the device of
FIG. 4;
[0035] FIG. 6 shows a schematic diagram of a conventional
multi-channel FP laser diode array of an external resonator
type;
[0036] FIG. 7 shows a schematic diagram of variations of incident
angles to the grating according to an array interval and a focal
distance; and
[0037] FIG. 8 shows a configuration of a conventional multi-channel
DFB laser diode array.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] In the following detailed description, only the preferred
embodiment of the invention has been shown and described, simply by
way of illustration of the best mode contemplated by the
inventor(s) of carrying out the invention. As will be realized, the
invention is capable of modification in various obvious respects,
all without departing from the invention. Accordingly, the drawings
and description are to be regarded as illustrative in nature, and
not restrictive.
[0039] FIG. 1 shows a schematic diagram of a multi-channel FP laser
diode array of an external resonator type according to a first
preferred embodiment of the present invention, and it uses the same
reference numerals as those of the conventional configurations
shown in FIGS. 4 to 8 so as to escape the need for repeated
descriptions.
[0040] A combiner 20 is inserted to an output end of a
multi-channel FP laser diode array 14, and a fiber 10 is provided
to an output end of the combiner 20. A light beam output from the
multi-channel FP laser diode array 14 is collimated while passing
through a lens 4 and diffracted and provided to a grating 6, and
the diffracted light beam is reflected again from a reflector 12
and fed back to the multi-channel FP laser diode array 14. The
combiner 20 does not use the light beam output from the 0-order
term of the grating 6 as an optical output, but uses a light beam
(the left side of the figure) output from each channel of the
multi-channel FP laser diode array 14, and accordingly, it is
convenient to arrange the combiner 20 with the fiber 10 and package
them.
[0041] Further, since the above configuration allows controlling a
tunable wavelength through an arrangement interval of the
multi-channel FP laser diode array 14 and a focal length of the
lens 4, and concurrently enables controlling the tunable wavelength
through rotation of the reflector 12 based on the diffraction
phenomenon of the grating, the above configuration realizes a wide
tunable wavelength range.
[0042] The combiner 20 has an optical passive waveguide coupler or
adopts an optical waveguide coupler of the MMI (multi-mode
interface) type.
[0043] The combiner 20 generates coupling loss in proportion to a
number of channels, and the MMI coupler remarkably causes the
coupling loss in the multi-channel configuration having more than
eight channels, but serious problems such as damage to the actual
use can be escaped through a careful design.
[0044] FIG. 2 shows a schematic diagram of a multi-channel FP laser
diode array of an external resonator type according to a second
preferred embodiment of the present invention. In this embodiment,
an AWG (array waveguide grating) 22 is used as the combiner 20.
[0045] The AWG 22 is a multiplexer having wavelength selectivity
for each output end, and it slightly differentiates channel lengths
of the array optical waveguide range on the light beams provided to
respective channels with the same interval. According to this
configuration, phase variation is generated while a light beam in a
medium is propagating, constructive or destructive interferences
occur in each output end, and hence, a specific wavelength is
selected and output to each output channel.
[0046] The AWG 22 has very low coupling loss characteristics
compared to the MMI coupler.
[0047] FIGS. 3(a) through 3(c) show spectral characteristics of
optical outputs caused by the multi-channel FP laser diode array
which adopts the AWG 22.
[0048] As shown, FIG. 3(a) shows that an FSR (free spectral range)
of the grating 6 is generated by rotation of the reflector 12, and
a spectral width is determined by the grating period and
format.
[0049] In this preferred embodiment, a wavelength interval between
channels can be controlled by an array interval of the
multi-channel FP laser diode 14 and a focal length of the lens
4.
[0050] FIG. 3(b) shows transmittivity characteristics of the AWG
22, and the FSR and the spectral width are determined according to
factors including a number of channels, lengths of optical
waveguides, and a refractive index in the AWG 22.
[0051] The above-noted configuration shows that optical outputs can
be corrected because of wavelength selectivity of the AWG even
though the wavelength selectivity is not accurate with respect to a
channel interval and rotation of the reflector in the case the
grating period is relatively wide, and indicates that no fine
tuning between a tuning mirror and an array element is needed,
thereby providing an excellent yield and element reliability.
[0052] FIG. 3(c) shows wavelength characteristics of optical
outputs generated by an output end of the AWG 22, showing that a
number N.times.M of channels is obtained when a number of channels
is N and rotation of the reflector is performed M times.
[0053] In the above-described device, the configuration by the AWG
22 requires no crosstalk and PDL (polarization dependent loss)
characteristics of the AWG, since the light beams output from laser
diode array have TE (transverse electric) polarization, thereby
easily realizing the device.
[0054] As described, since the tunable wavelength semiconductor
laser diode outputs optical outputs through the combiners,
arrangements with the fiber are easily executed. In particular,
since the usage of an AWG substantially reduces coupling loss, no
fine tuning of a reflector, arrangement interval of a multi-channel
FP laser diode array, or accuracy of a focal length of a lens are
required, thereby simplifying packaging and improving yields and
element reliabilities.
[0055] Since a multi-channel FP laser diode array is provided to a
external resonator type light source for generating a tunable
wavelength by rotation of a reflector, and one of a combiner is
added to an array output end, characteristics of continuous tunable
wavelengths, narrow widths, and high single modes are obtained,
packaging is easily performed, and stable variable wavelength
features are provided.
[0056] In addition, since no fining tuning of a reflector and
accuracy of an array interval and a focal distance are required,
yields and reliabilities are greatly enhanced.
[0057] While this invention has been described in connection with
what is presently considered to be the most practical and preferred
embodiment, it is to be understood that the invention is not
limited to the disclosed embodiments, but, on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims.
* * * * *